TOKYO — Taikichiro Mori is reputed to be the second-richest man in the world.

But one would never know it.

Last year, the quiet, 85-year-old real estate magnate came in second on Forbes magazine's list of the world's richest men with assets estimated at $18 billion, mostly fabulously expensive real estate in central Tokyo.

But Mori, who retains the air of the college professor he was until 30 years ago, does not spend lavishly.

He does not collect the objects the Japanese wealthy usually spend money on--antique tea ceremony bowls or expensive cars--and lives in a modest Tokyo apartment that one employee described as very ordinary.

"I don't think much about spending money," the balding Mori said in an interview. "Our household runs just like any other Japanese household.

"I live a life that leaves me content and happy."

Asked to compare himself to New York mogul Donald Trump, Mori said, "I prefer a more austere life style. That's what I'm used to, and I'm happy with it."

For all his wealth, Mori's life hasn't changed much since he was an economics professor at Yokohama City University.

"I haven't changed my spending patterns much since the days when I was a professor," he said. "I was used to living like a professor and I wasn't about to change."

Today he is driven by chauffeur to the office. But then, so is every other top Japanese executive.

Perhaps the biggest difference in his life style is that he no longer carries a wallet. For the past eight years or so he has worn only kimonos, which have no pockets.

His mode of dress is unusual in a country where the business suit is virtually de rigueur. "When I wear a necktie it confines my neck," Mori said.

Mori, who lives with his wife, has three sons and a daughter. Two of the sons work for him and the third is an engineering professor at prestigious Keio University in Tokyo.

Lately, reporters have beaten a path to the door of businessman Yoshiaki Tsutsumi, rated No. 1 on Fortune's list of the world's richest individuals with an estimated worth of $18.9 billion.

Far less known is Mori, the son of a rice dealer who owned several rental properties in central Tokyo. Mori took over the family real estate business in the 1950s and formed his own company in 1959 at the age of 55.

"Just acting as a landlord and collecting rents seemed too boring. I wanted to do something else with my education," Mori said, remembering his days as a professor.

Fire-bombing during World War II left the family's rental apartments--all wooden buildings--in smoking ruins.

But the family fortunes recovered in the 1950s, with Mori selling off property in less convenient locations and developing prime land into modern office buildings.

Like most of Japan's super-rich, Mori has cashed in on the Tokyo real estate boom, which has seen property values skyrocket during the past few years.

Today his company, Mori Building Co. Ltd., owns 79 high-rise buildings on some of the most valuable land in the world.

His pride and joy is a sparkling 13-acre office-and-apartment complex called Ark Hills in downtown Tokyo, based on the site of a traditional bath house owned by the Mori family.

The Mori group of companies made about $2.3 billion in 1988, virtually all of it rental payments.

Mori's latest project is the company's first departure from real estate--a night school aimed at professionals in architecture, city planning and related fields.

"There is a need for a company to provide education for employees," he said. "Young people today are getting smarter but leave a lot to be desired in morals and manners."